QOpenGLTextureBlitter Class Reference

The QOpenGLTextureBlitter class provides a convenient way to draw textured quads via OpenGL. More...

#include <qopengltextureblitter.h>

Collaboration diagram for QOpenGLTextureBlitter:

Public Types
enum	Origin { OriginBottomLeft , OriginTopLeft }
	\value OriginBottomLeft Indicates that the data in the texture follows the OpenGL convention of coordinate systems, meaning Y is running from bottom to top. More...

Public Member Functions
	QOpenGLTextureBlitter ()
	Constructs a new QOpenGLTextureBlitter instance.
	~QOpenGLTextureBlitter ()
	Destructs the instance.
bool	create ()
	Initializes the graphics resources used by the blitter.
bool	isCreated () const
void	destroy ()
	Frees all graphics resources held by the blitter.
bool	supportsExternalOESTarget () const
bool	supportsRectangleTarget () const
void	bind (GLenum target=GL_TEXTURE_2D)
	Binds the graphics resources used by the blitter.
void	release ()
	Unbinds the graphics resources used by the blitter.
void	setRedBlueSwizzle (bool swizzle)
	Sets whether swizzling is enabled for the red and blue color channels to swizzle.
void	setOpacity (float opacity)
	Changes the opacity to opacity.
void	blit (GLuint texture, const QMatrix4x4 &targetTransform, Origin sourceOrigin)
	Performs the blit with the source texture texture.
void	blit (GLuint texture, const QMatrix4x4 &targetTransform, const QMatrix3x3 &sourceTransform)
	Performs the blit with the source texture texture.

Static Public Member Functions
static QMatrix4x4	targetTransform (const QRectF &target, const QRect &viewport)
	Calculates a target transform suitable for blit().
static QMatrix3x3	sourceTransform (const QRectF &subTexture, const QSize &textureSize, Origin origin)
	Calculates a 3x3 matrix suitable as the input to blit().

Detailed Description

The QOpenGLTextureBlitter class provides a convenient way to draw textured quads via OpenGL.

Since

5.8

\inmodule QtOpenGL

Drawing textured quads, in order to get the contents of a texture onto the screen, is a common operation when developing 2D user interfaces. QOpenGLTextureBlitter provides a convenience class to avoid repeating vertex data, shader sources, buffer and program management and matrix calculations.

For example, a QOpenGLWidget subclass can do the following to draw the contents rendered into a framebuffer at the pixel position {(x, y)}:

void OpenGLWidget::initializeGL()
{
    m_blitter.create();
    m_fbo = new QOpenGLFramebufferObject(size);
}
 
void OpenGLWidget::paintGL()
{
    m_fbo->bind();
    // update offscreen content
    m_fbo->release();
 
    m_blitter.bind();
    const QRect targetRect(QPoint(x, y), m_fbo->size());
    const QMatrix4x4 target = QOpenGLTextureBlitter::targetTransform(targetRect, QRect(QPoint(0, 0), m_fbo->size()));
    m_blitter.blit(m_fbo->texture(), target, QOpenGLTextureBlitter::OriginBottomLeft);
    m_blitter.release();
}

The blitter implements GLSL shaders both for GLSL 1.00 (suitable for OpenGL (ES) 2.x and compatibility profiles of newer OpenGL versions) and version 150 (suitable for core profile contexts with OpenGL 3.2 and newer).

Definition at line 17 of file qopengltextureblitter.h.

Member Enumeration Documentation

Origin

enum QOpenGLTextureBlitter::Origin

\value OriginBottomLeft Indicates that the data in the texture follows the OpenGL convention of coordinate systems, meaning Y is running from bottom to top.

\value OriginTopLeft Indicates that the data in the texture has Y running from top to bottom, which is typical with regular, unflipped image data.

See also

blit()

Enumerator
OriginBottomLeft
OriginTopLeft

Definition at line 23 of file qopengltextureblitter.h.

Constructor & Destructor Documentation

QOpenGLTextureBlitter()

QOpenGLTextureBlitter::QOpenGLTextureBlitter

(

)

Constructs a new QOpenGLTextureBlitter instance.

Note

no graphics resources are initialized in the constructor. This makes it safe to place plain QOpenGLTextureBlitter members into classes because the actual initialization that depends on the OpenGL context happens only in create().

Definition at line 432 of file qopengltextureblitter.cpp.

~QOpenGLTextureBlitter()

QOpenGLTextureBlitter::~QOpenGLTextureBlitter

(

)

Destructs the instance.

Note

When the OpenGL context - or a context sharing resources with it - that was current when calling create() is not current, graphics resources will not be released. Therefore, it is recommended to call destroy() manually instead of relying on the destructor to perform OpenGL resource cleanup.

Definition at line 446 of file qopengltextureblitter.cpp.

References destroy().

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Member Function Documentation

bind()

void QOpenGLTextureBlitter::bind

(

GLenum

target = GL_TEXTURE_2D

)

Binds the graphics resources used by the blitter.

This must be called before calling blit(). Code modifying the OpenGL state should be avoided between the call to bind() and blit() because otherwise conflicts may arise.

target is the texture target for the source texture and must be either GL_TEXTURE_2D, GL_TEXTURE_RECTANGLE, or GL_OES_EGL_image_external.

See also

release(), blit()

Definition at line 581 of file qopengltextureblitter.cpp.

References QOpenGLShaderProgram::bind(), d, GL_FLOAT, QOpenGLTextureBlitterPrivate::Program::glProgram, and targetToProgramIndex().

Referenced by QOpenGLWindowPrivate::endPaint(), and QWaylandQuickCompositor::grabSurface().

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blit() [1/2]

void QOpenGLTextureBlitter::blit	(	GLuint	texture,
		const QMatrix4x4 &	targetTransform,
		const QMatrix3x3 &	sourceTransform )

Performs the blit with the source texture texture.

targetTransform specifies the transformation applied. This is usually generated by the targetTransform() helper function.

sourceTransform specifies the transformation applied to the source. This allows using only a sub-rect of the source texture. This is usually generated by the sourceTransform() helper function.

See also

sourceTransform(), targetTransform(), Origin, bind()

Definition at line 702 of file qopengltextureblitter.cpp.

References d, sourceTransform(), and targetTransform().

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blit() [2/2]

void QOpenGLTextureBlitter::blit	(	GLuint	texture,
		const QMatrix4x4 &	targetTransform,
		Origin	sourceOrigin )

Performs the blit with the source texture texture.

targetTransform specifies the transformation applied. This is usually generated by the targetTransform() helper function.

sourceOrigin specifies if the image data needs flipping. When texture corresponds to a texture attached to an FBO pass OriginBottomLeft. On the other hand, when texture is based on unflipped image data, pass OriginTopLeft. This is more efficient than using QImage::mirrored().

See also

targetTransform(), Origin, bind()

Definition at line 681 of file qopengltextureblitter.cpp.

References d, and targetTransform().

Referenced by clippedBlit(), QOpenGLWindowPrivate::endPaint(), and QWaylandQuickCompositor::grabSurface().

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create()

bool QOpenGLTextureBlitter::create

(

)

Initializes the graphics resources used by the blitter.

Returns

true if successful, false if there was a failure. Failures can occur when there is no OpenGL context current on the current thread, or when shader compilation fails for some reason.

See also

isCreated(), destroy()

Definition at line 461 of file qopengltextureblitter.cpp.

References QSurfaceFormat::CoreProfile, QOpenGLContext::currentContext(), d, QOpenGLContext::format(), fragment_shader, fragment_shader150, qMakePair(), QOpenGLTextureBlitterPrivate::TEXTURE_2D, texture_buffer_data, vertex_buffer_data, vertex_shader, and vertex_shader150.

Referenced by QOpenGLWindowPrivate::endPaint(), and QWaylandQuickCompositor::grabSurface().

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destroy()

void QOpenGLTextureBlitter::destroy

(

)

Frees all graphics resources held by the blitter.

Assumes that the OpenGL context, or another context sharing resources with it, that was current on the thread when invoking create() is current.

The function has no effect when the blitter is not in created state.

See also

create()

Definition at line 519 of file qopengltextureblitter.cpp.

References d, isCreated(), QOpenGLTextureBlitterPrivate::TEXTURE_2D, QOpenGLTextureBlitterPrivate::TEXTURE_EXTERNAL_OES, and QOpenGLTextureBlitterPrivate::TEXTURE_RECTANGLE.

Referenced by ~QOpenGLTextureBlitter(), and QOpenGLWindowPrivate::~QOpenGLWindowPrivate().

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isCreated()

bool QOpenGLTextureBlitter::isCreated

(

)

const

Returns

true if create() was called and succeeded. false otherwise.

See also

create(), destroy()

Definition at line 504 of file qopengltextureblitter.cpp.

References d, and QOpenGLTextureBlitterPrivate::TEXTURE_2D.

Referenced by destroy(), and QOpenGLWindowPrivate::endPaint().

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release()

void QOpenGLTextureBlitter::release

(

)

Unbinds the graphics resources used by the blitter.

See also

bind()

Definition at line 612 of file qopengltextureblitter.cpp.

References d, QOpenGLTextureBlitterPrivate::Program::glProgram, QOpenGLShaderProgram::release(), and targetToProgramIndex().

Referenced by QOpenGLWindowPrivate::endPaint(), and QWaylandQuickCompositor::grabSurface().

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setOpacity()

void QOpenGLTextureBlitter::setOpacity

(

float

opacity

)

Changes the opacity to opacity.

The default opacity is 1.0.

Note

the blitter does not alter the blend state. It is up to the caller of blit() to ensure the correct blend settings are active.

Definition at line 647 of file qopengltextureblitter.cpp.

References d.

setRedBlueSwizzle()

void QOpenGLTextureBlitter::setRedBlueSwizzle

(

bool

swizzle

)

Sets whether swizzling is enabled for the red and blue color channels to swizzle.

An BGRA to RGBA conversion (occurring in the shader on the GPU, instead of a slow CPU-side transformation) can be useful when the source texture contains data from a QImage with a format like QImage::Format_ARGB32 which maps to BGRA on little endian systems.

By default the red-blue swizzle is disabled since this is what a texture attached to an framebuffer object or a texture based on a byte ordered QImage format (like QImage::Format_RGBA8888) needs.

Definition at line 634 of file qopengltextureblitter.cpp.

References d.

sourceTransform()

QMatrix3x3 QOpenGLTextureBlitter::sourceTransform ( const QRectF & subTexture, const QSize & textureSize, Origin origin )

static

Calculates a 3x3 matrix suitable as the input to blit().

This is used when only a part of the texture is to be used in the blit.

subTexture is the desired source rectangle in pixels, textureSize is the full width and height of the texture data. origin specifies the orientation of the image data when it comes to the Y axis.

See also

blit(), Origin

Definition at line 753 of file qopengltextureblitter.cpp.

References QSize::height(), OriginTopLeft, QSize::width(), QPointF::x(), and QPointF::y().

Referenced by blit(), and clippedBlit().

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supportsExternalOESTarget()

bool QOpenGLTextureBlitter::supportsExternalOESTarget

(

)

const

Returns

true when bind() accepts GL_TEXTURE_EXTERNAL_OES as its target argument.

See also

bind(), blit()

Definition at line 538 of file qopengltextureblitter.cpp.

References QOpenGLContext::currentContext().

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supportsRectangleTarget()

bool QOpenGLTextureBlitter::supportsRectangleTarget

(

)

const

Returns

true when bind() accepts GL_TEXTURE_RECTANGLE as its target argument.

See also

bind(), blit()

Definition at line 550 of file qopengltextureblitter.cpp.

References QOpenGLContext::currentContext(), and qMakePair().

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targetTransform()

QMatrix4x4 QOpenGLTextureBlitter::targetTransform ( const QRectF & target, const QRect & viewport )

static

Calculates a target transform suitable for blit().

target is the target rectangle in pixels. viewport describes the source dimensions and will in most cases be set to (0, 0, image width, image height).

For unscaled output the size of target and viewport should match.

See also

blit()

Definition at line 722 of file qopengltextureblitter.cpp.

References viewport().

Referenced by blit(), blit(), clippedBlit(), and QOpenGLWindowPrivate::endPaint().

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The documentation for this class was generated from the following files:

• qtbase/src/opengl/qopengltextureblitter.h (05fc3aef53348fb58be6308076e000825b704e58)
• qtbase/src/opengl/qopengltextureblitter.cpp (135a792940ed3a7ed2cfc632e2b11477edea7706)